Nikolai Rimsky-Korsakov · section 36 of 96
The Minor Subdominant Chord and the Sixth Chord of the Second Degree in the Harmonic Major Mode
Read and hear this section in the playable edition →§ 35. — 1) In the major-key exercises that follow, the group of subdominant chords of the harmonic major mode may be used:
the minor triad of the fourth degree and its first inversion, and the sixth chord of the second degree with the fifth of the root lowered:

2) Do not use chromatic motion:

nor, in general, alternate too often within one phrase between the subdominant harmony of the natural major mode and that of the harmonic major mode.
3) Do not use the harmonic major mode when realizing chorales.
(*) Occasionally use the succession of the fifth and fourth degrees in the middle of the chorale.